1. Field of the Invention
The present invention relates to an ink jet printer.
2. Description of Related Art
Conventional ink jet printers are of the construction in which ink drops are ejected to the print paper through orifices formed in a nozzle plate. If dust is attracted on the nozzle plate, the dust jams the orifices resulting in missing dots in the print. This deteriorates print quality and may lead to a printer failure.
Therefore, a cleaning unit is usually provided at the home area of the ink jet head, so that the wiper of the cleaning unit wipes the dust from the nozzle plate when the ink jet head returns to the home area at predetermined time intervals during printing operation. FIG. 18 illustrates a general construction of a conventional ink jet printer.
Referring to FIG. 18, a print head 12 is held directly over print paper 11 which is transported it its path. The print head 12 is carried on a carriage 13 which is moved slidably on a guide shaft 14 extending transversely of the path and in parallel to the surface of the print paper 11. An endless belt 15 is disposed about the pulleys 15a and 15b which are connected to the shaft, not shown, of a spacing motor 16, and is securely connected to the carriage 13. When the spacing motor 16 drives the pulley 15a in rotation in directions shown by arrow, the pulleys 15a and 15b cause the belt 15 to run so that the carriage 13 carrying the print head 12 thereon is moved in directions shown by arrows A1 and A2.
The print head 12 is adapted to move both in a print area and in a home area. When the print head 12 is in the print area, the print head 12 performs printing operation by ejecting ink drops through the orifices to the print paper 11 while moving in the directions shown by arrows A1 and A2.
The print head 12 enters the home area at predetermined timings during printing operation, so that the dust trapped on the nozzle plate 12a is wiped off. The print head 12 also enters the home area after printing operation so as to cap the nozzle plate 12a to protect from the environment. For cleaning and capping purposes, a cleaning unit 21 is disposed at a location in the home area where the cleaning unit 21 opposes the guide shaft 14. The cleaning unit includes a wiper 17, holder 18, cap 19, and holder 20. The wiper 17 is supported by the holder 18 and wipes the dust off the nozzle plate 12a. The cap 19 is held by the holder 20 and closes the nozzle plate 12a to prevent the ink from drying when not printing.
The wiper 17 and cap 19 are formed or a resilient material such as rubber. The wiper 17 is moved in directions shown by arrows B1 and B2 to take tip an operation position and standby position, respectively. The cap 19 is moved in directions shown by arrows C1 and C2 to take up an operation position and standby position, respectively.
The wiping operation of the aforementioned construction will be described. FIGS. 19-22 illustrate a relevant part of the conventional ink jet printer. For clarity of explanation, the cap 19 and holder 20 have been omitted throughout FIGS. 19-22.
As shown in FIG. 19, the print head 12 is moved in the direction shown by arrow A1 and subsequently the wiper 17 is moved in the direction shown by arrow B1 to the operation position. Then, as shown in FIG. 20, the wiper 17 is stopped at a predetermined position relative to the shaft 14 while the print head 12 moves still further in the direction shown by arrow A1 to a position shown in FIG. 21 so that the dust on the nozzle plate 12a is wiped off. This completes a first stage of wiping operation.
Then, the print head 12 is moved in the direction shown by arrow A2 as shown in FIG. 22, so that the nozzle plate 12a is again wiped by the wiper 17. Then, the print head 12 moves still further in the direction shown by arrow A1, completing a second stage of wiping operation.
In this manner, the wiping operation is performed. Upon completion of the second stage of wiping operation, the wiper 17 is moved in the direction shown by arrow B2 (FIG. 18) so that the cleaning unit 21 enters its standby condition as shown in FIG. 19.
However, the aforementioned conventional ink jet printer suffers from the following disadvantages. The print head 12 moving in the directions shown by arrows A1 and A2 causes the wiper 17 to resiliently flex so that the wiper 17 causes tile ink to splash as the wiper 17 moves out of engagement with the print head 12 and resiliently regains its original shape. The splash of ink causes soiling of the interior of the ink jet printer and repetitive wiping operation causes the wiper 17 to wear.
One way of preventing the ink from splashing is to reduce the velocity of the print head 12 so that the wiper 17 slowly flexes when it moves into and out of engagement with the print head 12. However, reducing the velocity of the print head 12 decreases the amount of data printed by the printer per unit time, i.e., the throughput of the printer.